In general, a VCR is provided with a head drum assembly including a plurality of video heads, a rotary drum, a supporting shaft and a stationary drum. The video heads are fixed to the rotary drum rotatably supported through a pair of the bearings, i.e., a lower bearing and an upper bearing. Each of the bearings is of a sliding bearing type and has an outer peripheral side surface and an inner peripheral side surface. The outer peripheral side surface of each bearing is closely fitted into the rotary drum and the inner peripheral side surface of each bearing is rotatably fitted onto the supporting shaft.
The lower bearing, which is located at a lower part of the rotary drum, is also brought in contact with the supporting shaft and the stationary drum simultaneously. Since the lower bearing supports a radial and a thrust loads of the rotary drum simultaneously, the lower bearing may become overloaded, which, in turn, necessitates a need to lubricate with an oil to be retained in a bearing cavity concavely formed at the stationary drum.
The head drum assembly is used to read/write image signals recorded on a magnetic tape. The image signals are recorded on signal tracks of the magnetic tape. The signal tracks are inclined at a predetermined angle to a traveling direction of the magnetic tape to achieve a high recording density. In order to align the video heads with the signal tracks, the head drum assembly, and, hence the lower bearing, is mounted at the same angle of inclination as that of the signal tracks to a main frame of the VCR, resulting in an uneven distribution of the oil in the bearing cavity, i.e., one side of the bearing cavity having a greater amount of the oil than the opposite side. This may cause the oil to be non-uniformly spread between contact-surfaces of the lower bearing and the bearing cavity, preventing the lower bearing from rotating smoothly and forcing the rotary drum (to which the video heads are attached) to vibrate, which may, in turn, cause a jitter, i.e., screen shaking.